| 川西拉拉Fe-Cu矿区含矿镁铁质层状岩席的首次发现及其成岩成矿意义 |
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| 引用本文： | 孙君一,于文佳,唐泽勋,李重,罗照华.川西拉拉Fe-Cu矿区含矿镁铁质层状岩席的首次发现及其成岩成矿意义[J].地学前缘,2019,26(1):313-325. |
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| 作者姓名： | 孙君一 于文佳 唐泽勋 李重 罗照华 |
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| 作者单位： | 中国地质大学地质过程与矿产资源国家重点实验室,北京,100083;凉山矿业股份有限公司,四川凉山,615146 |
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| 基金项目： | 国家重点基础研究发展计划“973”项目(2011CB808901);国家自然科学基金委员会与俄罗斯基础研究基金会合作项目(RFBR14-05-91162-NSFC);中国地质调查局地质调查项目(1212011220921，1212011121266，12120113094100，1212011121075)；中国地质大学(北京)基本科研业务费专项资金资助项目(2-9-2015-412) |
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| 摘 要： | 尽管镁铁质层状侵入体得到了广泛关注,与其相关的成岩和成矿过程仍然存在很多疑问。文中首次报道了在川西拉拉Fe-Cu矿区发现的一种含矿镁铁质岩席,它的深入研究可能有助于理解拉拉Fe-Cu矿床的成因,以及层状侵入体的组装过程与成矿作用。野外观察表明,该岩席共由9个岩相带组成,相邻岩相带为侵入接触关系,上半部分和下半部分的岩性呈镜像对应。对该岩席上半部分的5个岩相带分别进行了显微镜观察、粉晶X-射线衍射分析和CSD分析,表明相邻岩相带的矿物组成和结构参数具有明显区别,揭示该岩席由4、5次岩浆脉动组装而成。各岩相带均具有显微斑状结构,其中1～4岩相带的斑晶矿物主要为角闪石、云母和Ti-Fe氧化物,第5岩相带的斑晶为白云母、钾长石和石英。此外,第3岩相带还含有大颗粒单斜辉石斑晶,第4岩相带含有方解石大斑晶。含水矿物呈斑晶产出表明所有岩相带都是挥发分(H2O+CO2)饱和或过饱和岩浆固结的产物,但各岩相带的岩浆具有不同的来源。根据斑晶(循环晶)矿物组合、定量化结构参数和参数变异趋势,推测拉拉岩席之下曾经存在3～5个位于不同深部水平上的岩浆房。这些岩浆房有不同成分的进化岩浆充填,可能富集了相应的成矿金属。当深部含矿流体输入该岩浆系统时,有可能引起骨牌效应,导致各种含矿流体大规模释放。拉拉矿区的这类岩席可能对成矿物质起到了屏蔽作用,使其大规模聚集形成超大型矿床。需要注意的是,拉拉岩席的富矿岩相带侵位时间最晚,类似于攀枝花铁矿。因此,拉拉岩席的成岩成矿模式有可能也适应于攀枝花式铁矿。
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| 关 键 词： | 拉拉Fe-Cu矿床 层状侵入体 成矿系统 透岩浆流体 定量化结构分析 |
| 收稿时间： | 2017-01-04 |
Discovery of the ore-bearing mafic layered sill in the Lala Fe-Cu ore district,western Sichuan Province,China and its implications for petrogenesis and metallogenesis |
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| SUN Junyi,YU Wenjia,TANG Zexun,LI Zhong,LUO Zhaohua.Discovery of the ore-bearing mafic layered sill in the Lala Fe-Cu ore district,western Sichuan Province,China and its implications for petrogenesis and metallogenesis[J].Earth Science Frontiers,2019,26(1):313-325. |
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| Authors: | SUN Junyi YU Wenjia TANG Zexun LI Zhong LUO Zhaohua |
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| Institution: | 1. State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China;
2. Liangshan Mining Industry CO. LTD, Liangshan 615146, China; |
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| Abstract: | The layered intrusion has received much attention, however, its petrogenensis and metallogenic model are still debatable. Here, we report for the first time the mafic ore-bearing layered intrusions in the Lala Fe-Cu ore district. This discovery will aid metallogenic research on the Fe-Cu ore, Lala district for a better understanding of the intrusion and metallogenic processes of layered intrusion. Field observation showed that the layered intrusion was composed of nine lithofacies zones, with intrusive contacts between adjacent zones and mirror imaging between the upper and lower halves of the facies. Microscopic observations, X-ray diffraction and CDC analyses of the upper five lithofacies zones indicated that the mineral composition and structural parameters of the adjacent facies zones were markedly different, which may suggest that the intrusion was formed by 45 pulsed invasions. Each lithofacies zone has the porphyritic texture. Phenocrysts in the 1st4th facies zones were mainly hornblende, mica and Ti-Fe oxide, while muscovite, potash feldspar and quartz mainly in the 5th , and big clinopyroxene and calcite phenocrysts made up the 3rd and 4th facies zones, respectively. The hydrous mineral in phenocryst implied that all ore-forming magmas contained saturated or supersaturated H2O + CO2 volatiles, but had different origin for each facies zone. Based on the phenocryst mineral assemblage, quantitative structural parameters and parameter variation trend, one can speculate that 35 magma chambers of different depths existed under the Lala sill. These magma chambers were packed with evolved magmas of varied compositions, possibly enriching the corresponding ore-forming metals. As the deep metallogenetic fluid entered this magmatic system, ensuing domino effect might lead to mass release of all kinds of metallogenetic fluids. The Lala-type sill might act as shield for the ore-forming materials to aggregate at a large scale and form super-size deposits. It is worth noting that the rich ore lithofacies zone experienced the latest emplacement, similar to that of the Panzhihua-type iron deposit. Therefore, the petro-metallogenetic model of the Lala sill may be applicable to the Panzhihua-type iron deposit. |
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| Keywords: | Lala Fe-Cu deposit layered intrusion mineral system transmagmatic fluid crystal size distribution
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